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Peiselulli
Registered: Oct 2006
Posts: 81 |
1541 low level programming problem
Hello,
I have a problem that I don't understand. I tried the
following code for the 1541 :
jsr $F97E ; MOTOR_ON
jsr $fe00 ; SET_READ_MODE
loop
BIT $1C00 ; SYNC signal
BMI loop ; not yet found?
LDA $1C01 ; read byte
lda $1c00
eor #$08
sta $1c00
CLV
-
bvc -
lda $1c01
jmp loop
I expect (if a floppy is inserted) that the LED flickers, but it does not. If I remove the "bvc" command, it works like expected. Has anybody a idea what I have forgotten to initialize ?
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Krill
Registered: Apr 2002
Posts: 2839 |
(Excuse my lame posting skillz)
This is from my loader:
waitsync: bit VIA2_T1C_H
bpl wsynctmout
bit VIA2_PRB
bmi waitsync
bit VIA2_PRA
clv
bvc *
ldx #$00
lda VIA2_PRA; is never $00 but usually $52 (header) or $55 (data)
clv
rts
It's pretty long ago, but i guess the read access to $1c01 (VIA2_PRA) after the sync and _before_ the first clv is mandatory for some reason.
May i ask what your experiments will eventually lead to? :) |
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Peiselulli
Registered: Oct 2006
Posts: 81 |
this experiments have no real aim, its just for getting more knowledge programming the 1541.
But the thing getting even more strange:
The following code did not work, but I see no really difference to your code:
loop
BIT $1C00 ; SYNC signal
bmi loop ; not yet found?
bit $1c01
clv
bvc *
lda $1c01
clv
ldy #$20
ldx #$00
-
inx
bne -
dey
bne -
lda $1c00
eor #$08
sta $1c00
jmp loop
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Krill
Registered: Apr 2002
Posts: 2839 |
Have you executed an SEI and are you really on a 1541 (and not a 1571 in 2mhz mode or so)? |
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Peiselulli
Registered: Oct 2006
Posts: 81 |
I am on a 1541-II and i have do a "sei" before.
I have the feeling that anything is missing for reading bytes
(because the sync bit works in write mode, too)
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Krill
Registered: Apr 2002
Posts: 2839 |
Hmm, if you're on a valid formatted track i don't see a reason for the routine to fail. It's stuck in the bvc loop, right? |
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Peiselulli
Registered: Oct 2006
Posts: 81 |
yes, it did.
is there something to initalize that i have forgotten ?
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Krill
Registered: Apr 2002
Posts: 2839 |
Also from my loader:
lda #CB2_OUTPUT_HIGH | CB1_IRQ_ON_NEG_ACTIVE_EDGE | CA2_OUTPUT_HIGH | CA1_IRQ_ON_NEG_ACTIVE_EDGE
sta VIA2_PCR
This is an lda #$ee sta $1c0c, maybe that fixes it? |
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Peiselulli
Registered: Oct 2006
Posts: 81 |
many thanks, that was missing !
now it flickers :->
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Krill
Registered: Apr 2002
Posts: 2839 |
Greatness :) |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
Also, I'd add a wait loop after turning the motor on. It takes some time until it has 100% speed.
Oh and for searching a sync, you can use the routine at $F556. |
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